Tape automated bonding (TAB) apparatus are commonly employed in conjunction with a pick and place device for populating an electronic circuit board with the components of one or more signal processing systems. A non-limiting example of such a TAB apparatus is described in the Ellis, U.S. Pat. No. 5,287,608, issued Feb. 27, 1994, assigned to the assignee of the present application and the disclosure of which is incorporated herein. As diagrammatically illustrated in FIG. 1, which essentially corresponds to FIG. 1 of the above-identified '608 patent, such an apparatus typically includes a part-excision, lead-forming station 12, to which an electronic circuit component that is to be excised from an associated part carrier 13, supplied by way of a carrier storage and supply magazine 11, is transported from a magazine/feed station 14 by means of a carrier shuttle (not shown), which is transported along a track 15. In order to excise the component from its carrier 13 and form the leads of the part for placement onto a circuit board, a pair of die members, comprised of a lower die member or anvil 21 and an upper die member 23, are arranged to be positioned at station 12.
To facilitate cycling between part excision, lead formation and seizure of the excised and formed part for placement on the circuit board, the lower die member/anvil 21 is mounted on a translatable platen 25, which is controllably cycled between the part-excision, lead-forming station 12 to which the part is delivered by the carrier shuttle, and a formed part pick-up station 17, where the excised and formed part is seized by the pick and place device for attachment to the circuit board. The upper die member 23 is positioned at the part-excision, lead-forming station 12, such that it will be aligned with the lower die member/anvil 21, when the lower die member/anvil 21 is returned from the formed part pick-up station 17 to station 12. With the two die members mutually aligned at station 12, a part that has been transported to station 12 is excised from its carrier and placed upon the anvil 21, so that its leads may be shaped in response to the operation of a die member actuator or press 30, which vertically translates the upper die member 23 downwardly into engagement with the part and the anvil 21. In order for the upper and lower die members to be brought into proper engagement with one another at station 12, it is necessary that they be maintained in precise alignment during vertical downward translation of the upper die member 23 onto the anvil 21.
For this purpose, as diagrammatically illustrated in FIG. 2, it is customary practice to mount a plurality of alignment bearing shafts 31 on the lower surface 33 of the upper die member 23, and a plurality of bushings 41 on the upper surface 43 of the lower die member/anvil 21. As shown in greater detail in FIG. 3, each alignment bearing shaft 31 has a ball bearing-containing sleeve or cage 35, having ball bearings 37 that are rotatably translatable along shaft 31. To prevent ball bearing-containing sleeve 35 from coming off the lower end 32 of shaft 31, a retaining element, in the form of a C-clamp 34 is captured within an annular groove 36 adjacent to the lower end 32 of the shaft 31.
Ball bearing-retaining sleeve 35 is sized to be insertable into the bore 40 of a respective bushing 41 on the lower die member 21, so that, when the upper and lower die members are brought together, sleeve 35 will enter the bushing 41 and thereafter guide the shaft 31 vertically downward into the bushing. As a consequence, during its vertical travel, the upper die member 23 will be maintained parallel to the lower die member/anvil 21, thus ensuring proper engagement of the die members with the part.
Because of the very close tolerances of the dimensions of the ball bearings 37, shaft 31 and the interior bore of the bushings 41, in order to realize successful downward travel engagement of the upper die member 23 with the lower die member 21 (provided by insertion of the shafts 31 into bushings 41), it is necessary that the axes of the bearing shafts 31 extending from the bottom surface of the upper die member 23 be very precisely aligned (effectively coaxial) with the axes of the bushings of the lower die member 21. Such alignment has been conventionally carried out by hand, with a TAB machine operator performing a `look and feel` handling of the die members until the alignment shafts of the upper die are inserted into and fully seated in the bushings of the lower die. In the course of this exercise it has been observed that very slight angular offsets of the alignment shaft and bushing axes will cause the lower edges of the ball bearing-retaining sleeves to become caught or bind in the bores of the bushings, and thereby prevent the sleeves from being readily inserted into the bushings. As a result, very delicate handling of the two die members is required.
Once the upper and lower die members have been aligned with one another, it is further necessary to accurately position the die members relative to the die actuator at the part-excision, lead-forming station. It is not until this two-fold die member assembly and positioning task is performed that the apparatus is ready to excise and form parts. Thus, machine set-up is labor intensive and time consuming. In addition, whenever a die changeover is carried out, this procedure must be repeated for the replacement die members.